This invention relates to a method and apparatus for transverse cutting of multi-ply web material and, more particularly, to a continuous motion saw. A continuous motion saw is designed to cut a product in motion. Illustrative products are "logs" of bathroom tissue and kitchen toweling, and bolts or continuous superposed plies of facial tissue, interfolded or otherwise.
The illustrative products, for example, are produced at high speed on machines termed "reminders". These machines start with a parent roll perhaps about 10 feet (2.3 meters) long and about 8 feet (1.9 meters) in diameter--resulting from the output of a paper-making machine. The parent roll is unwound to provide a web which can be transversely perforated and then rewound into retail size rolls of at least 3.5 inches (89 mm) in diameter for bathroom tissue and kitchen toweling, viz. a cross-sectional area of 9.6 in.sup.2 (6190 mm.sup.2). Conventional high speed automatic rewinders can produce upwards of 30 logs per minute. These logs then are delivered to a log saw where they are moved axially for severing into retail size lengths. In the case of facial tissue, the product may be continuous (as in co-owned U.S. Pat. No. 4,052,048) and this also requires transverse cutting at regular intervals. In this case, the minimum cross-sectional area is at least 3.5 in.sup.2 (2200 mm.sup.2).
Saws for making bathroom tissue, kitchen toweling, etc. started being used in the middle 1950s principally for toilet tissue and have come to be known as "log saws". Prior to that time, the retail size rolls were made by slitting the web on the rewinder. For example, spaced slitting wheels are shown operating against a slitting roll in co-owned U.S. Pat. No. 2,769,600. This proved unsatisfactory. When the wide web being processed had holes stemming from manufacture on the paper machine, slitting would cause at least one of the narrower webs to jam the rewinder. This required shutdown and cleaning out the jam. To avoid this recurring problem of dealing with "fish-eyes" in the web, the web was rewound as a log. So, to cut the log into the retail size lengths, a log saw was needed.
The first commercially successful log saw was the "Gilbertville" saw of Gage, U.S. Pat. No. 2,752,999. This saw operated intermittently--swinging downwardly and upwardly (in knife-like fashion) against the log which was indexed a product length (41/2" for bathroom tissue) while the saw disc was lifted upwardly away from the log path. Sharpening of the saw disc occurred also when the disc was upwardly out of the log path.
The next commercially successful log saw is seen in co-owned U.S. Pat. No. 3,213,731. This differed from the Gilbertville saw in having the saw disc move through an orbit--passing through the log or logs at the nadir of the orbit. Sharpening occurred when the disc was upwardly out of the path. However, as with the Gilbertville saws, the operation was still intermittent--only having the saw cut the log after it had been indexed the appropriate distance.
The next major development was in the mid-1970s with the use of the continuous motion (CM) saw as seen in co-owned U.S. Pat. No. 4,041,813. This differed in two major respects from the prior log saws. The log was advanced continuously and the saw was orbited continuously. This was achieved by having the orbit axis skewed relative to the path of log travel. The angle of skew was of the order of a few degrees--sufficient to accommodate the space in between cuts. After the '813 patent was granted, the German counterpart was rejected on art relating to cigarette making machines. Thereafter, the '813 patent was reissued as RE. 30,598. Representative of the cigarette making machine were U.S. Pat. Nos. 1,630,132 and 1,846,942.
The next commercial machine did not appear until the early 1990s as seen in U.S. Pat. No. 5,315,907. This was stated to be an improvement on the '813 patent. It did not utilize any of the teachings of the cigarette-making machine publication. In the competitive '907 patent, the saw head was reciprocated parallel to the log length between cuts.
The instant invention makes use of a 4-bar linkage somewhat analogous to that of the cigarette-making machines of the 1920s which heretofore had not been considered applicable to log saws. For example, a log saw disc blade has an orbit diameter of at least about 30 inches (750 mm) while the blade (not necessarily a disc) of a cigarette machine has an orbit diameter of about 6" (150 mm). A more significant difference resides in the product. In converted paper products, the cross-sectional area is at least 3.5 in.sup.2 (2400 mm.sup.2) while cigarettes have a cross-sectional area of about 0.07 in.sup.2 (45 mm.sup.2). So, the instant invention builds on the concept of the '813 patent which has been satisfactory in handling the conventional high speed automatic rewinders which produce upwards of 30 logs per minute. However, the '813 saw was not readily alterable to provide different length products.
For product length change, the skew angle had to be changed. This required replacement of the blade mounting and drive components. In particular, the angle of the block mounting of the blade had to be changed to return the blades back to perpendicular and the beveled gears inside it--that were used to drive the blade--had to be changed to continue to match the angled housing. With the inventive saw, there is no such onerous replacement. For that matter, there was a complicated routine involved in product length change in the competitive saw of the '907 patent.
According to the inventive method of operating an orbital saw to transversely sever superposed elongated web plies into shorter length products, the first step is to advance superposed elongated web plies along a linear path, then providing a 4-bar linkage including first and second bar means extending generally parallel to each other and third and fourth bar means or brackets connecting the first and second bar means adjacent the ends thereof, further providing a disc blade rotatably mounted on each of the third and fourth bar means with each of the third and fourth bar means being equipped with means for rotating the disc blades, then rotating the first bar means of the 4-bar linkage about a first axis to orbit the blades with the blade orbit intersecting the linear path with the centers of the disc blades being at least 36" (914 mm) apart, while skewing the first axis at a minor acute angle to the linear path, connecting the first and second bar means with the third and fourth bar means to provide at least one degree of pivotal freedom of the third and fourth bar means relative to the first and second bar means, and rotating the second bar means about a second axis different from the first axis to compensate for the skewing and also to orient the disc blades perpendicular to the web plies in the linear path when severing the web plies.
The invention is described in conjunction with illustrative embodiments in the accompanying drawing.